VOIP

Introduction
One of the main driving factors for deploying Voice over IP (VoIP) networks isthe cost benefit associated with doing so.This chapter introduces the reader tothis concept and the Cisco IP Telephony solution.The chapter presents examplesof cost justification and some return on investment (ROI) scenarios.In this chapter you will also be introduced to some exciting advanced VoIPfeatures such as Web integration,multimedia integration,and telephony applica-tion programming interfaces (TAPI).
Introduction to Voice Over IP

Welcome to the new world of packetized voice! Although the idea of packetizedvoice might not be new,we now have the integrated solutions to make ithappen.This text provides you with a thorough understanding of Cisco’s currentvoice solutions,with an emphasis on current! The VoIP industry is a rapidlyevolving one,perhaps changing even faster than the Internet.Keep this guide as areference for voice integration possibilities,but always keep abreast of the latesttechnologies.What is hot today will be commonplace tomorrow.The objectives for this chapter are to:Establish the basic differences between circuit-switched and packet-switched networks.Build a needs and cost justification for toll-bypass solutions.Explore the opportunities for replacing the traditional private branchexchange (PBX) with the Cisco IP Telephony system.Review software integration possibilities such as TAPI integration.Understand the link layer VoIP technologies such as voice over FrameRelay (VoFR) and voice over asynchronous transfer mode (VoATM).Scattered throughout this chapter are several diagrams of network design con-cepts.Later in this book we delve into much greater detail regarding specificequipment and configuration issues.This first chapter focuses on the opportuni-ties that arise from moving to a packetized voice architecture.Along with man-agement and maintenance enhancements,we look at the all-important dollar.Most companies have spent exorbitant amounts of money to install andmaintain their PBXs.Packetizing voice allows for tremendous cost savings nowand in the future.As more standards are ratified,the cost of setting up a VoIP network continues to drop.This is quite a different model from the traditionalPBX cost trends of the last few decades.This chapter explores how to go aboutbuilding an ROI proposal that in most cases will justify a conversion to packe-tized voice.We specifically discuss Cisco’s VoIP solution,known as Cisco IPTelephony (CIPT).We explore link layer VoIP technologies such as VoFR andVoATM.These are just the tip of the iceberg.As VoIP becomes more widespreadand ubiquitous,we will begin to see applications that we can’t even imagine yet.Moving voice from a closed proprietary system to an open standards-based archi-tecture will revolutionize the phone industry and the world as much as theInternet has in terms of communication and the way business is transacted.

Common VoIP Implementation Services

Today’s PSTN is based on the transmission of analog signals over switched circuits.In contrast,VoIP networks send digitized voice over a packet-based network.Aswe shall see,VoIP networks can offer telephony services at compelling prices.

Toll Bypass

Relative to the Internet,the PSTN offers voice services with expensive charges,or tolls.Toll bypassis the avoidance of PSTN charges by using data networks,suchas the Internet,to carry voice conversations.Figure 1.2 shows a simple exampleof toll bypass using gateways that are capable of providing an interface betweenan IP network and a traditional PBX.

VoFR

Voice over frame relay (VoFR)is the use of a Frame Relay network to carry IPpackets containing digitized voice packets.IP phones and voice-capable switchesor routers may be hooked up to this Frame Relay network to digitize voice sig-nals and place them into IP packets.The IP packets are carried to their destina-tions via the Frame Relay network.

VoATM

Voice over asynchronous transfer mode (VoATM)is the use of an ATM network tocarry digitized voice packets.Instead of carrying variable-length frames,an ATMnetwork carries small fixed-length frames called cells.Each cell is 53 bytes longand contains a 5-byte header and a 48-byte payload.In an ATM network,theVoIP packet is segmented and placed inside these cells.The small fixed ATM cellsize offers many advantages.Its small size means that the latency or delay as thecell passes through an ATM switch is very short.In contrast,the store-and-for-ward delay of an IP packet through a router is much longer because the last bit ofthe packet must be received before the first bit can be transmitted.ATM switches are extremely fast,and the quality of service offered by ATMnetworks can be very high.In addition,ATM offers various class of service (CoS)options such as constant bit rate (CBR) that was designed specifically for trans-porting voice and other real-time protocols.CBR provides a better quality ofservice by minimizing time variations in the transmission of voice cells,a phe-nomenon known as jitte

Point-to-Point Links

The use of point-to-point links to interconnect a company’s offices allows acompany to build and administer its own private network.Using VoIP overpoint-to-point links allows a common IP staff to operate both voice and datatransmission services.Common link layer protocols used on point-to-point linksare High-Level Data Link Control (HDLC) and Point-to-Point Protocol (PPP).

Cisco IP Telephony

The VoIP portion of the evolving Cisco Architecture for Voice,Video,andIntegrated Data (AVVID) is Cisco IP Telephony,or CIPT.CIPT is the corner-stone of Cisco’s VoIP solution and is fast replacing traditional PBXs.Let’s discussCIPT’s major components.

Cisco IP Telephony Clients

Telephones capable of digitizing voice signals are known as IP telephony clientsorsimply IP phones.They contain digital signal processors (DSPs) to perform thisfunction.Cisco offers a variety of such IP telephony clients.In particular,theCisco IP Phone 7960 and IP Phone 7940 are feature-rich and include smallliquid crystal display (LCD) displays,control buttons,and multiline capabilities.The Cisco IP Conference Station 7935 is an IP conference phone.

IP Softphones

The Cisco IP SoftPhone is a virtual telephone that runs in a Windows desktopPC or laptop.IP softphonesare personal computers that contain software to allowthem to operate as IP telephony clients.The PCs contain speakers and micro-phones that can operate similarly to a telephone handset.In addition,the IP tele-phony software digitizes the voice signals and sends the voice packets across theIP network.Softphones provide a rich environment for development ofTAPIapplications,such as Web click-to-talk.

Cisco Call Manager

The Cisco Call Manager (CCM) is a software call-processing application thatruns on a Cisco Media Convergence Server (MCS).The CCM takes the place ofa PBX and performs several key functions:Registering IP telephony devicesCall processingAdministering dial plans and route plans Managing resourcesA group or pair of redundant call managers can support up to 2500 users.Acluster of redundant call manager groups can support up to 10,000 telephony users.In the Cisco IP telephony schema,call managers perform the functions tradi-tionally performed by PBXs.As we shall see,being software-based,the CCM canbe continually enhanced to provide features beyond those traditionally providedby PBXs.